Personal computers are equipped with graphics capabilities, which the user can control with commands in Basic language. This permits making line drawings which are displayed on the monitor screen. The fundamental principle is to define, in Cartesian coordinates of x and y, the location of a point where a line starts, and the location for its end. Circles can be displayed by entering the appropriate command and specifying the location of its center, with its radius. However, circles, and other curves are actually executed by multiple short straight line segments, so that a circle is really a multi-sided polygon.
The coordinates entered during the creation of a drawing can be stored in the memory chips of the computer, if desired.
A variety of software programs are now available, such as Versacad 5.0, developed by Versacad Corporation, Huntington Beach, CA, which greatly extend the graphics capability described above. The origin of a two dimensional coordinate system can be placed anywhere on the monitor screen, and a large selection of image elements, such as a line, a circle, or a rectangle, can be selected from a menu. The size and placement of these elements are entered by specifying their x and y coordinates. The coordinates can be entered in a variety of ways, including by keyboard, by joystick, by a probe with a digitizing tablet, or by a `mouse`.
These picture elements can be moved around, combined, and otherwise manipulated as required, to produce any desired drawing.
Vendors offer add-on software, extending the capabilities of the 2D systems.
It is the custom of CAD vendors to use the term 3D for what should be correctly called perspective drawings. Herein the term 3D will be retained in references to prior art, but the correct term will be applied to the product of this invention.
Current 3D systems first produce what has been called "wire drawings", in which hidden detail is mingled with the desired visible, then the computer calculates which lines to retain and which should be erased, then finally removing the unwanted lines to produce a solid appearance. This is inefficient, requiring (1) the input of data which is later discarded, (2) a complex program capable of distinguishing between the required visible and the unwanted invisible lines, and (3) finally performing the erasure. All of this requiring a large computer memory, and is wasteful of human and computer time.
This invention discloses a method for producing an accurate perspective drawing of an object. While it can be used with a personal computer, or even by pencil and paper, it is especially adapted to be operated in conjunction with a modified CAD system.
The geometrical and mathematical steps which comprise this invention converts an original set of data, employed for the usual orthogonal elevation and plan views, into a second set of data used to make the perspective drawing.
Hence, it can be understood this invention is not a computer program, but is a method comprised of a series of steps, well adapted to be executed by a relatively short program segment inserted into a commercially available CAD software system.
The software of all commercial CAD systems are carefully guarded trade secrets, but the general fundamentals, described elsewhere in this disclosure are well known. Since different programmers will differ in the program they may write to accomplish a given task, there can be a variety of routines by which this method can be integrated into a particular CAD system.